Breaking news from TechPowerUp a very short time ago has it that unfortunately ATI will not make the release date of their R600 cards within Q1 2007 after all.

The briefing from the Techpowerup crew goes on to say that AMD's reasoning behind this further delay is that they dont feel the development of the card is quite at the stage they want it to be just yet, and they're still tinkering with it a bit more to make sure it delivers in a big way come time for launch (which will now be an undetermined date in Q2 sometime).

XBit Labs also have a dedicated article up on the news here.

just got off the phone with ATI who informed me that the Editor's Day which was scheduled around March 11 (flights and hotels were already booked) has been postponed to the second quarter of 2007.
The reason is that their R600 Series is not where they want it to be yet, so they decided to move the launch to be able to deliver a competitive product. Also I am hearing that at the Q2 launch we will see more than just GPU related stuff, so I would guess Physics or GPGPU computing.